1. Field of the Invention
The present invention generally relates to controlling power demand in an electric power distribution system and, in particular, to a system and method for ordering power demand reductions at customer premises through an integrated wireless communication network.
2. Related Art
Electric utilities and other organizations are responsible for supplying an economic, reliable and safe source of electricity to customers. The electric utility or other responsible organization, through its energy delivery system, provides to its customers electricity at a suitable voltage and frequency. This electricity is provided on an instantaneous basis. That is, when the customer turns on the light switch to light a room, the electric utility or other responsible organization provides the electricity to the customer's light bulb the instant that the customer flips the light switch on.
One of the well known difficulties in providing electricity to customers is precisely matching the aggregate amount of electricity consumed by all of the customers on an instantaneous basis with the amount of electricity generated and/or purchased by the providing electric utility or other responsible organization. That is, at any instant in time, the electric utility or other responsible organization must provide exactly the amount of electricity used by all of the customers (plus the associated transmission system losses). The total amount of electricity used by all of the customers at any given instant in time is commonly referred to as demand. Demand typically is measured in units of watts, kilo-watts (kW), mega-watts (MW) or the like. For example, a conventional light bulb may have a demand of 60 watts. One thousand of these light bulbs has a demand of 6 kW. If all one thousand of these light bulbs are all turned on at the same instant in time, the electric utility or other responsible organization must instantly provide an additional 6 kW of electricity (in addition to any associated increases in transmission system losses) by increasing generation or purchases.
Failure by the electric utility or other responsible organization to exactly match the electric demand of their customers with the supply (generation and purchases), during every instant in time, may have very undesirable consequences should the mismatch become significant. When significant mismatches between demand and supply occur, distortions in the electric system frequency occurs. Although the electric system components are designed to operate when the electric frequency is slightly distorted, protective devices coupled to selected components in the electric system are designed to operate to automatically reduce or eliminate significant mismatches between demand and supply. Furthermore, other electricity characteristics may be undesirably distorted, such as voltage, such that other types of protective relays begin to operate.
For example, if the electric utility or other responsible organization loses a generator in an unplanned manner, the electric system demand will exceed supply (because the supply decreases when the generator shuts down). If the mismatch is sufficiently large, the electric frequency will decrease from its nominal value of 60 hertz (Hz). If the frequency drops to below 59.8 Hz, relays sense the frequency decay and operate to selectively disconnect predefined groups of customers from the energy delivery system. That is, power is shut off to some customers. Thus, demand is reduced, hopefully to the point where demand again approximately equals supply such that the frequency recovers back to its nominal 60 Hz value. Disconnecting customer loads to arrest frequency decay is known as load shedding.
Although the action of the frequency sensitive relays effectively arrests the undesirable frequency decay, thereby saving the energy delivery system from a more severe decay in frequency and other undesirable associated problems, those customers that were disconnected are impacted in an undesirable manner. That is, the customers who were selected to participate in the load shedding scheme had their power shut off. The affected customers are inconvenienced when they are disconnected from the energy delivery system, and the affected customers did not volunteer to be selected as participants in the load shedding scheme. Furthermore, the electric utility or other responsible organization loses the associated sales to the affected customers, thereby negatively impacting the electric utility's or other responsible organization's revenue stream.
Electric utilities and the other responsible organizations have implemented a variety of techniques to decrease the frequency of occurrence of these undesirable mismatches between energy demand and supply. One well known technique is to couple selected energy consuming appliances to radio frequency (RF) controlled receivers. Then, when a mismatch in demand and supply occurs, or when the electric utility or other responsible organization anticipates that a mismatch occurrence is eminent, the electric utility or other responsible organization orders the shut off of the selected energy consuming appliances by transmitting a shut-off signal via a RF signal to the RF receivers. Typically, a group of appliances are coordinated to respond to a single RF frequency or a single command delivered to the RF receivers. Such a group of aggregated appliances is commonly referred to as a load block. Thus, by issuing a single shut-off command, appliances in the entire load block can be shut off such that a meaningful decrease in demand occurs.
Participation in such a load block is typically voluntary. Often, customers are offered incentives to participate. For example, a customer can be given a decrease in rate and/or a rebate to voluntarily allow the utility or other responsible organization to couple an RF receiver to their appliance.
For example, a load block can be formed by coupling each one of the above described one thousand light bulbs to RF receivers such that a 6 kW demand reduction is realized (assuming that all of the light bulbs were on prior to sending the shut-off command). However, this is not a very effective technique for reducing demand. The 6 kW decrease in demand does not provide a meaningful demand reduction because the demand decrease is too small to be of practical help in matching demand of the entire system with supply. Also, the cost of the RF receivers is not likely justifiable for so little of a demand reduction.
On the other hand, forming a load block by connecting one hundred air conditioning units may provide a meaningful technique of reducing demand in a controlled manner. For example, if each air conditioning unit, when on, consumes approximately 10 kW, the electric utility or other responsible organization can reduce demand by as much as 1.0 MW. A 1.0 MW demand reduction is sufficiently large to make a meaningful reduction in system demand. Even if only a portion of the air conditioning units were on at the time the shut-off command was transmitted to the RF receivers, the demand reduction may still be sufficiently large to be meaningful.
Typically, electric utilities or other responsible organizations having such RF controlled energy demand reduction schemes will have a plurality of load blocks that can be selectively shut off depending upon the particular needs at hand. For example, a load block may be designed to provide an expected demand reduction of 5 MW. The system may have eight such blocks. At some point in time, the electric utility or other responsible organization may determine that a 5 MW demand reduction is needed for a two hour period. The eight load blocks would be sequentially shut off for fifteen minute intervals over the two hour period. Such an approach is desirable in that the negative impact to the customers will be minimized since the temperature of the customers' premises is not likely to become noticeably uncomfortable during the 15 minute period that their air conditioners are shut off.
Similarly, the electric utility or other responsible organization may determine that a 40 MW demand reduction is required for fifteen minutes, thereby providing sufficient time to increase generation or purchase additional power. All eight load blocks could be simultaneously shut off, thereby achieving a 40 MW demand reduction. One skilled in the art will appreciate the significant flexibility provided to the electric utility or other responsible organization having access to an energy demand reduction system employing a plurality of RF controlled load blocks.
However, such energy demand reduction systems employing a plurality of RF controlled load blocks have numerous problems and deficiencies. Once a load block is established by configuring an RF communication network to provide a unique shut-off signal, and after a sufficient number of selected appliances are fitted with RF receivers responsive to the shut-off signal, it is difficult to revise, update and/or modify the load block. If the shut-off signal is modified or changed, each individual appliance RF receiver may have to be manually reconfigured. If the amount of the load in the load block is to be changed, individual appliances and/or their RF receivers would have to be added, removed and/or reconfigured on an individual basis. Such changes require the time of a trained technician. Technician time directly equates to an expense to the electric utility or other responsible organization. Furthermore, making significant changes to an established load block will take a considerable amount of time to implement.
Furthermore, there is no way to ascertain the failure of an RF receiver or the associated appliance control equipment. Thus, the shut-off signal sent out to the RF receivers would not have an effect on a failed RF receiver. Only during a manual inspection would the failed RF receiver be detected and fixed.
Another problem associated with conventional RF controlled load blocks arises from the statistical nature of loads serviced by an electric power distribution system. Consider the above described scenario where each one hundred air conditioning units are each in a different residence. During a hot summer day, it is not probable that all one hundred of the air conditioning units will be on all at the same time. An air conditioning unit cycles on and off as needed to maintain temperature of the house according to a temperature range specified by the thermostat in the house. Thus, at any given moment, some of the air conditioners will likely be on and some of the air conditioners will likely be off. Furthermore, the thermostat settings will not be the same for all of the residences. Statistics are used by the electric utility or other responsible organization to estimate, with a reasonable degree of accuracy, how many of the air conditioning units will likely be on at any give instant for an ambient temperature. Thus, the amount of load consumed by the aggregation of the one hundred air conditioners can be estimated. However, an estimate is not an exact number. The electric utility or other responsible organization cannot know with certainty exactly how much load is shut off when the shut-off signal is sent out to the RF receivers.
Another related problem arises from the nature in which the loads are metered (measured). Typically, aggregate customer loads are metered on a real-time basis by monitoring meters residing in the distribution substations. Thus, if the load block is serviced from a single substation (which is not very likely), the electric utility or other responsible organization may get a good approximation of the effect of shutting off the load block by closely monitoring the substation meters. However, other loads are coming on, and going off, at precisely the same time that the shut-off signal is communicated to the load block. So, the meter will, to some degree, falsely imply that shutting off the load block had more, or had less, of an impact than what was in fact achieved by shutting off the load block. For example, the shut-off signal may shut off seventy-five of the one hundred air conditioning units in the load block (twenty five units are not running at the instant that the shut-off signal is sent). However, five air conditioning units not part of the load block may cycle on at substantially the same time that the shut-off signal is transmitted to the load block (a probable event if the substation is providing service to a large number of homes on a hot day). The substation meter would incorrectly imply that only seventy air conditioning units were shut off, when in fact, seventy-five air conditioning units were shut off. Thus, the electric utility or other responsible organization may at best have a good approximation of the effectiveness of shutting off a load block. But, the electric utility or other responsible organization will not know the exact amount of demand reduction realized when the load block is shut off.
Yet another problem with demand reduction systems employing fixed-size load blocks is that it is difficult to readjust changes made in demand, or to fine-tune the demand changes actually realized. A load block is pre-configured to affect a predetermined number of customer appliances (which may or may not actually be operating at any given instant in time). Thus, a load block designed to statistically provide a 10 MW demand reduction cannot be easily reconfigured to provide a 12 MW demand reduction. Furthermore, if a 10 MW demand reduction is desired, the load block designed to statistically provide a 10 MW demand reduction will probably never provide exactly a 10 MW demand reduction. If, for example, the load block provides an actual load reduction of 9 MW, there is no convenient and effective mechanism to fine tune the energy demand reduction system or the load block such that an additional 1 MW demand reduction can be ordered.
Thus, a heretofore unaddressed need exists in the industry for providing a demand reduction and control system that accurately indicates the true amount of demand reduction realized when a shut-off signal is transmitted. Also, there is a heretofore unaddressed need in the industry to provide a demand reduction and control system that provides for real time adjustment of demand on an appliance-by-appliance basis. There is also a heretofore unaddressed need in the industry to automatically detect failure of RF receivers so that repairs can be initiated.